While the pie dough chills, spread the sliced tomatoes over a triple layer of paper towels placed on a rimmed baking sheet and sprinkle with ¼ teaspoon salt. Let sit 30 minutes (longer is fine), then blot the tomatoes dry with more paper towels, and flip them over onto a fresh stack of paper towels. Sprinkle the second sides with ¼ teaspoon salt and let sit 30 minutes. Blot dry.

Let the dough stand at room temperature until slightly softened, 5 minutes in a warm kitchen OR 15 minutes in a cool kitchen. Sandwich the dough between 2 large pieces of parchment paper dusted lightly with oat flour, and gently begin pressing it flat, then roll it into a 12 by 16-inch (30 by 40-cm) rectangle. As you work, periodically peel back the top piece of parchment, dust the dough lightly with oat flour, replace the parchment, grasp the dough sandwich with both hands and flip the whole thing over. Peel off the new top piece of parchment, dust with flour and continue to roll. If the dough is uneven, cut off the long bits and press them onto the short bits, rolling to adhere. When your rectangle measures 12 by 16 inches (30 by 40 cm), trim the sides so that they’re even and straight. If your dough becomes soft or sticky at any point, slip it onto a baking sheet, parchment and all, and chill it for 10–20 minutes to firm the butter.

When the crust is rolled out, slide the dough onto a baking sheet (unrimmed if you’ve got one), still on the parchment, and chill until firm, 20 minutes.

Remove the dough from the refrigerator and brush the whole thing with a thin layer of beaten egg. Leaving a 1 ½ -inch rim on all sides, sprinkle evenly with the grated mozzarella, parmesan, and oregano. Layer the sliced, drained tomatoes over the top, overlapping them slightly, using only as many will fit in a single layer. Fold the dough edges over to form a crust, and brush with the beaten egg.

Transfer the tart to the oven and bake in the Baking Oven until the crust is golden and the filling bubbles, 40-50 minutes, peeking under the crust to make sure it isn’t burning toward the end. While the tart bakes, stir together the olive oil and garlic.

Remove the tart from the oven, drizzle with the garlic oil and a sprinkle of flaky salt and pepper, and finish with some oregano leaves. Cut the tart into rectangles and serve warm.

The tart is best within a few hours of baking, but leftovers keep well, refrigerated airtight, for up to 3 days. Reheat slices in a cast iron skillet set over a low flame; this will help the bottom crust crisp.

Recipe and images from https://bojongourmet.com/2017/08/rustic-heirloom-tomato-tart-gluten-free/